Magnetic memory element with multilayered seed structure

ABSTRACT

The present invention is directed to a magnetic structure, which includes a magnetic fixed layer structure formed on top of a seed layer structure. The seed layer structure includes one or more layers of a first transition metal, which may be platinum, palladium, nickel, or iridium, interleaved with one or more layers of a second transition metal, which may be tantalum, titanium, vanadium, molybdenum, chromium, tungsten, zirconium, hafnium, or niobium. The magnetic fixed layer structure has a first invariable magnetization direction substantially perpendicular to a layer plane thereof and includes layers of a first magnetic material interleaved with layers of the first transition metal. The first magnetic material may be made of cobalt.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of the commonlyassigned application bearing Ser. No. 15/687,258 filed on Aug. 25, 2017,entitled “Magnetic Structure with Multilayered Seed,” which is acontinuation-in-part of the commonly assigned application bearing Ser.No. 15/491,220 filed on Apr. 19, 2017, entitled “Perpendicular MagneticFixed Layer with High Anisotropy,” and a continuation-in-part of thecommonly assigned application bearing Ser. No. 15/295,002 filed on Oct.17, 2016, entitled “Magnetic Random Access Memory with Multilayered SeedStructure,” which is a continuation of the commonly assigned applicationbearing Ser. No. 14/687,161 filed on Apr. 15, 2015, entitled “MagneticRandom Access Memory with Multilayered Seed Structure,” which claims thebenefit of the provisional application bearing Ser. No. 62/001,554 filedon May 21, 2014, entitled “Magnetic Random Access Memory withMultilayered Seed Structure.” All of these applications are incorporatedherein by reference in their entirety, including their specificationsand drawings.

BACKGROUND

The present invention relates to a magnetic random access memory (MRAM)device, and more particularly, to a magnetic memory element includingmultiple magnetic layers having magnetization directions perpendicularto layer planes thereof.

Spin transfer torque magnetic random access memory (STT-MRAM) is a newclass of non-volatile memory, which can retain the stored informationwhen powered off. An STT-MRAM device normally comprises an array ofmemory cells, each of which includes at least a magnetic memory elementand a selection element coupled in series between appropriateelectrodes. Upon application of a switching current to the magneticmemory element, the electrical resistance of the magnetic memory elementwould change accordingly, thereby switching the stored logic in therespective memory cell.

FIG. 1 shows a conventional memory element for an STT-MRAM devicecomprising a magnetic reference layer 50 and a magnetic free layer 52with an insulating tunnel junction layer 54 interposed therebetween,thereby collectively forming a magnetic tunnel junction (MTJ) 56. Themagnetic reference layer 50 and free layer 52 have magnetizationdirections 58 and 60, respectively, which are substantiallyperpendicular to the layer planes. Therefore, the MTJ 56 is aperpendicular type comprising the magnetic layers 50 and 52 withperpendicular anisotropy. Upon application of a switching current to theperpendicular MTJ 56, the magnetization direction 60 of the magneticfree layer 52 can be switched between two directions: parallel andanti-parallel with respect to the magnetization direction 58 of themagnetic reference layer 50. The insulating tunnel junction layer 54 isnormally made of a dielectric material with a thickness ranging from afew to a few tens of angstroms. When the magnetization directions 60 and58 of the magnetic free layer 52 and reference layer 50 aresubstantially parallel (i.e., same direction), electrons polarized bythe magnetic reference layer 50 can tunnel through the insulating tunneljunction layer 54, thereby decreasing the electrical resistance of theperpendicular MTJ 56. Conversely, the electrical resistance of theperpendicular MTJ 56 is high when the magnetization directions 58 and 60of the magnetic reference layer 50 and free layer 52 are substantiallyanti-parallel (i.e., opposite directions). Accordingly, the stored logicin the magnetic memory element can be switched by changing themagnetization direction 60 of the magnetic free layer 52.

One of many advantages of STT-MRAM over other types of non-volatilememories is scalability. As the size of the perpendicular MTJ 56 isreduced, however, the thermal stability of the magnetic layers 50 and52, which is required for long term data retention, also degrades withminiaturization of the perpendicular MTJ 56. While the thermal stabilityof the perpendicular MTJ 56 may be improved by increasing the coercivityof the magnetic free layer 52, doing so may adversely increase thecurrent required to switch the magnetization direction 60 of themagnetic free layer 52.

For the foregoing reasons, there is a need for an MRAM device that has athermally stable perpendicular MTJ memory element which can beprogrammed with a low switching current.

SUMMARY

The present invention is directed to a memory element that satisfiesthis need. An MTJ memory element having features of the presentinvention comprises a magnetic free layer structure including one ormore magnetic free layers that have a variable magnetization directionsubstantially perpendicular to layer planes thereof; an insulatingtunnel junction layer formed adjacent to the magnetic free layerstructure; a magnetic reference layer structure formed adjacent to theinsulating tunnel junction layer opposite the magnetic free layerstructure, the magnetic reference layer structure including one or moremagnetic reference layers that have a first invariable magnetizationdirection substantially perpendicular to layer planes thereof; ananti-ferromagnetic coupling layer formed adjacent to the magneticreference layer structure opposite the insulating tunnel junction layer;a magnetic fixed layer structure formed adjacent to theanti-ferromagnetic coupling layer opposite the magnetic reference layerstructure, the magnetic fixed layer structure having a second invariablemagnetization direction that is substantially perpendicular to a layerplane thereof and is substantially opposite to the first invariablemagnetization direction; and a seed layer structure that may include afirst seed layer formed adjacent to the magnetic fixed layer structureand a second seed layer. The magnetic fixed layer structure includeslayers of a first type material interleaved with layers of a second typematerial with at least one of the first and second type materials beingmagnetic. The first seed layer may include one or more layers of nickelinterleaved with one or more layers of a first transition metal, whichmay be tantalum, titanium, or vanadium. The second seed layer may bemade of an alloy or compound comprising nickel and a second transitionmetal, which may be chromium, tantalum, or titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a cross-sectional view of a conventional magnetic tunneljunction;

FIG. 2 is a schematic circuit diagram of an MRAM array in accordancewith an embodiment of the present invention;

FIG. 3 is a schematic circuit diagram of an MRAM array in accordancewith another embodiment of the present invention;

FIG. 4 is a schematic circuit diagram of an MRAM array in accordancewith still another embodiment of the present invention;

FIGS. 5A and 5B are cross-sectional views of MTJ memory elements inaccordance with embodiments of the present invention;

FIGS. 6A-6G are cross-sectional views of exemplary magnetic free layerstructures in accordance with embodiments of the present invention;

FIGS. 7A-7G are cross-sectional views of exemplary magnetic referencelayer structures in accordance with embodiments of the presentinvention;

FIGS. 8A-8G are cross-sectional views of exemplary magnetic fixed layerstructures in accordance with embodiments of the present invention;

FIGS. 9A-9D are cross-sectional views of exemplary multilayer structurescomprising one or more stacks of a bilayer unit structure;

FIGS. 10A-10I are cross-sectional views of exemplary multilayerstructures comprising one or more stacks of a trilayer unit structure;

FIG. 11 is a cross-sectional view of an exemplary multilayer structurecomprising one or more stacks of a quadlayer unit structure;

FIGS. 12A-12D are cross-sectional views of exemplary seed layerstructures in accordance with embodiments of the present invention;

FIGS. 13A-13D are cross-sectional views of exemplary multilayerstructures comprising one or more stacks of a bilayer unit structure forthe seed layer;

FIGS. 14A-14D are cross-sectional views of exemplary cap layerstructures in accordance with embodiments of the present invention; and

FIG. 15 is a cross-sectional view of an exemplary structure for an MTJmemory element in accordance with an embodiment of the presentinvention.

For purposes of clarity and brevity, like elements and components willbear the same designations and numbering throughout the Figures, whichare not necessarily drawn to scale.

DETAILED DESCRIPTION

In the Summary above and in the Detailed Description, and the claimsbelow, and in the accompanying drawings, reference is made to particularfeatures (including method steps) of the invention. It is to beunderstood that the disclosure of the invention in this specificationincludes all possible combinations of such particular features. Forexample, where a particular feature is disclosed in the context of aparticular aspect or embodiment of the invention, or a particular claim,that feature can also be used, to the extent possible, in combinationwith and/or in the context of other particular aspects and embodimentsof the invention, and in the invention generally.

Where reference is made herein to a material AB composed of element Aand element B, the material AB can be an alloy, a compound, or acombination thereof, except where the context excludes that possibility.

The term “noncrystalline” means an amorphous state or a state in whichfine crystals are dispersed in an amorphous matrix, not a single crystalor polycrystalline state. In case of state in which fine crystals aredispersed in an amorphous matrix, those in which a crystalline peak issubstantially not observed by, for example, X-ray diffraction can bedesignated as “noncrystalline.”

The term “superlattice” means a synthetic periodic structure formed byinterleaving layers of at least two constituent materials. Asuperlattice has at least two repeated unit stacks with each unit stackformed by laminating the constituent materials. Because of the periodicnature of its structure, a superlattice may exhibit characteristicsatellite peaks when analyzed by diffraction methods, such as X-raydiffraction and neutron diffraction. For example, a [Co/Pt]_(n)superlattice would denote a structure formed by n stacks of the bilayerstructure of cobalt (Co) and platinum (Pt).

The term “magnetic dead layer” means a layer of supposedly ferromagneticmaterial that does not exhibit a net magnetic moment in the absence ofan external magnetic field. A magnetic dead layer of several atomiclayers may form in a magnetic film in contact with another layermaterial owing to intermixing of atoms at the interface. Alternatively,a magnetic dead layer may form as thickness of a magnetic film decreasesto a point that the magnetic film becomes superparamagnetic.

The term “at least” followed by a number is used herein to denote thestart of a range beginning with that number, which may be a range havingan upper limit or no upper limit, depending on the variable beingdefined. For example, “at least 1” means 1 or more than 1. The term “atmost” followed by a number is used herein to denote the end of a rangeending with that number, which may be a range having 1 or 0 as its lowerlimit, or a range having no lower limit, depending upon the variablebeing defined. For example, “at most 4” means 4 or less than 4, and “atmost 40%” means 40% or less than 40%. When, in this specification, arange is given as “a first number to a second number” or “a firstnumber-a second number,” this means a range whose lower limit is thefirst number and whose upper limit is the second number. For example,“25 to 100 nm” means a range whose lower limit is 25 nm and whose upperlimit is 100 nm.

FIG. 2 is a schematic circuit diagram of an MRAM array 100 in accordancewith an embodiment of the present invention. The MRAM array 100comprises a plurality of memory cells 102, each of the memory cells 102including a selection transistor 104 coupled to an MTJ memory element106; a plurality of parallel word lines 108 with each being coupled togates of a respective row of the selection transistors 104 in a firstdirection; and a plurality of parallel bit lines 110 with each beingcoupled to a respective row of the MTJ memory elements 106 in a seconddirection substantially perpendicular to the first direction; and aplurality of parallel source lines 112 with each being coupled tosources or drains of a respective row of the selection transistors 104in the second direction. The MTJ memory element 106 has a perpendicularMTJ structure that includes multiple magnetic layers havingmagnetization directions substantially perpendicular to layer planesthereof.

FIG. 3 is a schematic circuit diagram of an MRAM array 120 in accordancewith another embodiment of the present invention. The MRAM array 120comprises a plurality of memory cells 122 with each of the memory cells122 including a two-terminal selector 124 coupled to an MTJ memoryelement 106 in series; a first plurality of parallel wiring lines 126with each being coupled to a respective row of the MTJ memory elements106 in a first direction; and a second plurality of parallel wiringlines 128 with each being coupled to a respective row of the selectors124 in a second direction substantially perpendicular to the firstdirection. Accordingly, the memory cells 122 are located at the crosspoints between the first and second plurality of wiring lines 126 and128. The first and second plurality of wiring lines 126 and 128 may beword lines and bit lines, respectively, or vice versa. The MTJ memoryelement 106 may have a perpendicular MTJ structure that includesmultiple magnetic layers having magnetizations directions substantiallyperpendicular to layer planes thereof. Multiple layers of the memoryarray 120 may be stacked to form a monolithic three-dimensional memorydevice. While the MTJ memory element 106 is shown to form above thetwo-terminal selector 124 in FIG. 3, the stacking order of the MTJmemory element 106 and the selector 124 may reversed as illustrated inFIG. 4.

An embodiment of the present invention as applied to the MTJ memoryelement 106 will now be described with reference to FIG. 5A. Referringnow to FIG. 5A, the exemplary magnetic structure for the MTJ memoryelement 106 includes a magnetic tunnel junction (MTJ) structure 130 inbetween a seed layer structure 132 and a cap layer structure 134. TheMTJ structure 130 comprises a magnetic free layer structure 136 and amagnetic reference layer structure 138 with an insulating tunneljunction layer 140 interposed therebetween, an anti-ferromagneticcoupling layer 142 formed adjacent to the magnetic reference layerstructure 138 opposite the insulating tunnel junction layer 140, and amagnetic fixed layer structure 144 formed adjacent to theanti-ferromagnetic coupling layer 142 opposite the magnetic referencelayer structure 138. Therefore, the magnetic fixed layer structure 144is anti-ferromagnetically exchange coupled to the magnetic referencelayer structure 138 via the anti-ferromagnetic coupling layer 142. Themagnetic fixed layer structure 144 and the magnetic free layer structure136 may be formed adjacent to the seed layer structure 132 and cap layerstructure 134, respectively. Additional layers, magnetic ornon-magnetic, may form between the magnetic fixed layer structure 144and the seed layer structure 132 and/or between the magnetic free layerstructure 136 and the cap layer structure 134.

The magnetic free layer structure 136 has a variable magnetizationdirection 146 substantially perpendicular to a layer plane thereof. Themagnetic reference layer structure 138 has a first invariablemagnetization direction 148 substantially perpendicular to a layer planethereof. The magnetic fixed layer structure 144 has a second invariablemagnetization direction 150 that is substantially perpendicular to alayer plane thereof and is substantially opposite to the firstinvariable magnetization direction 148.

The stacking order of the layers 136-144 in the MTJ structure 130 of theexemplary structure of the memory element 106 may be inverted asillustrated in FIG. 5B. The exemplary structure of FIG. 5B includes anMTJ structure 130′ that has the same layers but with the invertedstacking order comparing to the MTJ structure 130. Accordingly, themagnetic free layer structure 136 and the magnetic fixed layer structure144 may be formed adjacent to the seed layer structure 132 and cap layerstructure 134, respectively.

The magnetic free layer structure 136 may include one or more magneticlayers with each layer having the variable magnetization direction 146as illustrated by the exemplary embodiments shown in FIGS. 6A-6G. FIG.6A shows that the magnetic free layer structure 136 includes a firstmagnetic free layer 152, which has the variable magnetization direction146, formed adjacent to the tunnel junction layer 140.

FIG. 6B shows the magnetic free layer structure 136 including a firstmagnetic free layer 152 formed adjacent to the tunnel junction layer 140and a second magnetic free layer 154 formed adjacent to the firstmagnetic free layer 152 opposite the tunnel junction layer 140. Each ofthe first and second magnetic free layers 152 and 154 has the variablemagnetization direction 146. The exemplary magnetic free layer structureof FIG. 6B may further include a non-magnetic perpendicular enhancementlayer (PEL) 158 interposed between the first and second magnetic freelayers 152 and 154 as illustrated in FIG. 6D.

The magnetic free layer structure 136 may include three magnetic freelayers 152-156 as illustrated in FIG. 6C. A first magnetic free layer152 is formed adjacent to the tunnel junction layer 140. A thirdmagnetic free layer 156 is formed adjacent to the first magnetic freelayer 152 opposite the tunnel junction layer 140. A second magnetic freelayer 154 is formed adjacent to the third magnetic free layer 156opposite the first magnetic free layer 152. Each of the first, second,and third magnetic free layers 152-156 has the variable magnetizationdirection 146.

The exemplary magnetic free layer structure of FIG. 6C may furtherinclude a non-magnetic perpendicular enhancement layer (PEL) 158interposed between the first and third magnetic free layers 152 and 156as illustrated in FIG. 6E. Alternatively, the exemplary magnetic freelayer structure of FIG. 6C may further include a non-magneticperpendicular enhancement layer (PEL) 158 interposed between the secondand third magnetic free layers 154 and 156 as illustrated in FIG. 6F.The exemplary magnetic free layer structure of FIG. 6F may be furthermodified to include a fourth magnetic free layer 160, which has thevariable magnetization direction 146, interposed between thenon-magnetic PEL 158 and the second magnetic free layer 154 asillustrated in FIG. 6G.

The exemplary magnetic free layer structures of FIGS. 6A-6G may beformed above the tunnel junction layer 140 as shown in FIG. 5A, orbeneath the tunnel junction layer 140 as shown in FIG. 5B. In the lattercase, the stacking sequence of the layers in the exemplary magnetic freelayer structures of FIGS. 6A-6G will be inverted.

The magnetic free layer structure 136 is not limited to the exemplarystructures of FIGS. 6A-6G and may have other structures that includemultiple magnetic free layers and optionally one or more PELs. Forexample, the magnetic free layer structure 136 may include four magneticfree layers in contiguous contact without any PEL.

The magnetic reference layer structure 138 may include one or moremagnetic layers with each layer having the first invariablemagnetization direction 148 as illustrated by the exemplary embodimentsshown in FIGS. 7A-7G. FIG. 7A shows that the magnetic reference layerstructure 138 includes a first magnetic reference layer 162, which hasthe first invariable magnetization direction 148, formed between thetunnel junction layer 140 and the anti-ferromagnetic coupling layer 142.

FIG. 7B shows the magnetic reference layer structure 138 including afirst magnetic reference layer 162 formed adjacent to the tunneljunction layer 140 and a second magnetic reference layer 164 formedadjacent to the first magnetic reference layer 162 opposite the tunneljunction layer 140. The anti-ferromagnetic coupling layer 142 is formedadjacent to the second magnetic reference layer 164 opposite the firstmagnetic reference layer 162. Each of the first and second magneticreference layers 162 and 164 has the first invariable magnetizationdirection 148. The exemplary magnetic reference layer structure of FIG.7B may further include a non-magnetic perpendicular enhancement layer(PEL) 168 interposed between the first and second magnetic referencelayers 162 and 164 as illustrated in FIG. 7D.

The magnetic reference layer structure 138 may include three magneticreference layers 162-166 as illustrated in FIG. 7C. A first magneticreference layer 162 is formed adjacent to the tunnel junction layer 140.A third magnetic reference layer 166 is formed adjacent to the firstmagnetic reference layer 162 opposite the tunnel junction layer 140. Asecond magnetic reference layer 164 is formed adjacent to the thirdmagnetic reference layer 166 opposite the first magnetic reference layer162. The anti-ferromagnetic coupling layer 142 is formed adjacent to thesecond magnetic reference layer 164 opposite the third magneticreference layer 166. Each of the first, second, and third magneticreference layers 162-166 has the first invariable magnetizationdirection 148.

The exemplary magnetic reference layer structure of FIG. 7C may furtherinclude a non-magnetic perpendicular enhancement layer (PEL) 168interposed between the first and third magnetic reference layers 162 and166 as illustrated in FIG. 7F. Alternatively, the exemplary magneticreference layer structure of FIG. 7C may further include a non-magneticperpendicular enhancement layer (PEL) 168 interposed between the secondand third magnetic reference layers 164 and 166 as illustrated in FIG.7E. The exemplary magnetic reference layer structure of FIG. 7E may befurther modified to include a fourth magnetic reference layer 170, whichhas the first invariable magnetization direction 148, interposed betweenthe non-magnetic PEL 168 and the second magnetic reference layer 164 asillustrated in FIG. 7G.

The exemplary magnetic reference layer structures of FIGS. 7A-7G may beformed beneath the tunnel junction layer 140 as shown in FIG. 5A, orabove the tunnel junction layer 140 as shown in FIG. 5B. In the lattercase, the stacking sequence of the layers in the exemplary magneticreference layer structures of FIGS. 7A-7G will be inverted.

The magnetic reference layer structure 138 is not limited to theexemplary structures of FIGS. 7A-7G and may have other structures thatinclude multiple magnetic reference layers and optionally one or morePELs. For example, the magnetic reference layer structure 138 mayinclude four magnetic reference layers in contiguous contact without anyPEL.

The magnetic fixed layer structure 144 may include one or more magneticlayers with each layer having the second invariable magnetizationdirection 150 as illustrated by the exemplary embodiments shown in FIGS.8A-8G. FIG. 8A shows that the magnetic fixed layer structure 144includes a first magnetic fixed layer 172, which has the secondinvariable magnetization direction 150, formed adjacent to theanti-ferromagnetic coupling layer 142.

FIG. 8B shows the magnetic fixed layer structure 144 including a firstmagnetic fixed layer 172 formed adjacent to the anti-ferromagneticcoupling layer 142 and a second magnetic fixed layer 174 formed adjacentto the first magnetic fixed layer 172 opposite the anti-ferromagneticcoupling layer 142. Each of the first and second magnetic fixed layers172 and 174 has the second invariable magnetization direction 150. Theexemplary magnetic fixed layer structure of FIG. 8B may further includea non-magnetic perpendicular enhancement layer (PEL) 178 interposedbetween the first and second magnetic fixed layers 172 and 174 asillustrated in FIG. 8D.

The magnetic fixed layer structure 144 may include three magnetic fixedlayers 172-176 as illustrated in FIG. 8C. A first magnetic fixed layer172 is formed adjacent to the anti-ferromagnetic coupling layer 142. Athird magnetic fixed layer 176 is formed adjacent to the first magneticfixed layer 172 opposite the anti-ferromagnetic coupling layer 142. Asecond magnetic fixed layer 174 is formed adjacent to the third magneticfixed layer 176 opposite the first magnetic fixed layer 172. Each of thefirst, second, and third magnetic fixed layers 172-176 has the secondinvariable magnetization direction 150.

The exemplary magnetic fixed layer structure of FIG. 8C may furtherinclude a non-magnetic perpendicular enhancement layer (PEL) 178interposed between the first and third magnetic fixed layers 172 and 176as illustrated in FIG. 8F. Alternatively, the exemplary magnetic fixedlayer structure of FIG. 8C may further include a non-magneticperpendicular enhancement layer (PEL) 178 interposed between the secondand third magnetic fixed layers 174 and 176 as illustrated in FIG. 8E.The exemplary magnetic fixed layer structure of FIG. 8E may be furthermodified to include a fourth magnetic fixed layer 180, which has thesecond invariable magnetization direction 150, interposed between thenon-magnetic PEL 178 and the second magnetic fixed layer 174 asillustrated in FIG. 8G.

The exemplary magnetic fixed layer structures of FIGS. 8A-8G may beformed beneath the anti-ferromagnetic coupling layer 142 as shown inFIG. 5A, or above the anti-ferromagnetic coupling layer 142 as shown inFIG. 5B. In the latter case, the stacking sequence of the layers in theexemplary magnetic fixed layer structures of FIGS. 8A-8G will beinverted.

The magnetic fixed layer structure 144 is not limited to the exemplarystructures of FIGS. 8A-8G and may have other structures that includemultiple magnetic fixed layers and optionally one or more PELs. Forexample, the magnetic fixed layer structure 144 may include fourmagnetic fixed layers in contiguous contact without any PEL.

The magnetic layers 152-156, 160-166, 170-176, and 180 may be made ofany suitable magnetic materials or structures. One or more of themagnetic layers 152-156, 160-166, 170-176, and 180 may comprise one ormore ferromagnetic elements, such as but not limited to cobalt (Co),nickel (Ni), and iron (Fe), to form a suitable magnetic material, suchas but not limited to Co, Ni, Fe, CoNi, CoFe, NiFe, or CoNiFe. Thesuitable magnetic material for the one or more of the magnetic layers152-156, 160-166, 170-176, and 180 may further include one or morenon-magnetic elements, such as but not limited to boron (B), titanium(Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum(Ta), chromium (Cr), molybdenum (Mo), tungsten (W), aluminum (Al),silicon (Si), germanium (Ge), gallium (Ga), oxygen (O), nitrogen (N),carbon (C), platinum (Pt), palladium (Pd), ruthenium (Ru), samarium(Sm), neodymium (Nd), antimony (Sb), iridium (Ir) or phosphorus (P), toform a magnetic alloy or compound, such as but not limited tocobalt-iron-boron (CoFeB), iron-platinum (FePt), cobalt-platinum (CoPt),cobalt-platinum-chromium (CoPtCr), cobalt-iron-boron-titanium (CoFeBTi),cobalt-iron-boron-zirconium, (CoFeBZr), cobalt-iron-boron-hafnium(CoFeBHf), cobalt-iron-boron-vanadium (CoFeBV),cobalt-iron-boron-tantalum (CoFeBTa), cobalt-iron-boron-chromium(CoFeBCr), cobalt-iron-titanium (CoFeTi), cobalt-iron-zirconium(CoFeZr), cobalt-iron-hafnium (CoFeHf), cobalt-iron-vanadium (CoFeV),cobalt-iron-niobium (CoFeNb), cobalt-iron-tantalum (CoFeTa),cobalt-iron-chromium (CoFeCr), cobalt-iron-molybdenum (CoFeMo),cobalt-iron-tungsten (CoFeW), cobalt-iron-aluminum (CoFeAl),cobalt-iron-silicon (CoFeSi), cobalt-iron-germanium (CoFeGe),iron-zirconium-boron (FeZrB), samarium-cobalt (SmCo),neodymium-iron-boron (NdFeB), cobalt-iron-antimony (CoFeSb),cobalt-iron-iridium (CoFeIr), or cobalt-iron-phosphorous (CoFeP).

Some of the above-mentioned magnetic materials, such as Fe, CoFe, CoFeBmay have a body-centered cubic (BCC) lattice structure that iscompatible with the halite-like cubic lattice structure of MgO, whichmay be used as the insulating tunnel junction layer 140. CoFeB alloyused for one or more of the magnetic layers 152-156, 160-166, 170-176,and 180 may contain more than 40 atomic percent Fe or may contain lessthan 30 atomic percent B or both.

One or more of the magnetic layers 152-156, 160-166, 170-176, and 180may alternatively have a multilayer structure formed by interleaving oneor more layers of a first type of material 182 with one or more layersof a second type of material 184 with at least one of the two types ofmaterials being magnetic, as illustrated in FIGS. 9A-9D. FIG. 9A showsan exemplary multilayer structure formed by one (n=1) or more stacks ofa bilayer unit structure 186, which includes a layer of the first typeof material 182 and a layer of the second type of material 184. Themultilayer structure for one or more of the magnetic layers 152-156,160-166, 170-176, and 180 may include additional layers formed at theperiphery of the exemplary multilayer structure of FIG. 9A. For example,the stacks of the bilayer unit structure 186 may include another layerof the second type of material 188 formed adjacent to the first type ofmaterial of the first stack as shown in FIG. 9B, or another layer of thefirst type of material 190 formed adjacent to the second type ofmaterial of the n^(th) stack (the end stack) as shown in FIG. 9C, orboth as shown in FIG. 9D. The layer of the first type of material 182 ina stack 186 may have a different thickness compared with other layers ofthe first type of material in other stacks. Similarly, the layer of thesecond type of material 184 in a stack 186 may have a differentthickness compared with other layers of the second type of material inother stacks. The layer thicknesses of the first type of material 190and the second type of material 188 at the periphery may or may not besame as the layer thicknesses of the first type of material 182 and thesecond type of material 184 of the bilayer unit structure 186,respectively. One or more layers of the two layers of materials 182 and184 may be extremely thin and thus have fragmented coverage and/or areperforated with holes. The stacking sequences of the exemplarymultilayer structures of FIGS. 9A-9D may be inverted.

The first type of material 182 and 190 may comprise one or moreferromagnetic elements, such as but not limited to cobalt (Co), nickel(Ni), and iron (Fe), to form a suitable magnetic material, such as butnot limited to Co, Ni, Fe, CoNi, CoFe, NiFe, or CoNiFe. The second typeof material 184 and 188 may be made of any suitable material, such asbut not limited to Pt, Pd, Ni, Ir, Cr, V, Ti, Zr, Hf, Nb, Ta, Mo, W,NiCr, NiV, NiTi, NiZr, NiHf, NiNb, NiTa, NiMo, NiW, or any combinationthereof. Therefore, one or more of the magnetic layers 152-156, 160-166,170-176, and 180 may include a multilayer structure, such as but notlimited to [Co/Pt], [Co/Pd], [Co/Pt(Pd)], [Co/Ni], [Co/Ir], [CoFe/Pt],[CoFe/Pd], [CoFe/Pt(Pd)], [CoFe/Ni], [CoFe/Ir], [Co/NiCr], or anycombination thereof. The multilayer structure may have a face-centeredcubic (FCC) type of lattice structure, which is different from thebody-centered cubic structure (BCC) of some ferromagnetic materials,such as Fe, CoFe, and CoFeB, and the halite-like cubic lattice structureof magnesium oxide (MgO) that may be used as the insulating tunneljunction layer 140. All individual magnetic layers of a magneticmultilayer structure may have the same magnetization direction. Themultilayer structure may or may not exhibit the characteristic satellitepeaks associated with superlattice when analyzed by X-ray, neutrondiffraction, or other diffraction techniques.

One or more of the magnetic layers 152-156, 160-166, 170-176, and 180may alternatively have a multilayer structure formed by one (n=1) ormore stacks of a trilayer unit structure 192 as illustrated in FIG. 10A.Each trilayer unit structure 192 includes a layer of a first type ofmaterial 194 and a layer of a third type of material 198 with a layer ofa second type of material 196 interposed therebetween. At least one ofthe three types of materials 194-198 is magnetic. The multilayerstructure of FIG. 10A may include one or more additional layers formedadjacent to the first stack and/or the n^(th) stack thereof. FIGS.10B-10E show some exemplary structures in which one or more additionallayers are formed adjacent to the first stack. The exemplary structuresof FIGS. 10C and 10E respectively show that a layer of the third type ofmaterial 200 and a layer of the second type of material 202 may formadjacent to the layer of the first type of material 194 of the firststack. The exemplary structure of FIG. 10C may further include a layerof the second type of material 202 formed adjacent to the layer of thethird type of material 200 opposite the first stack as shown in FIG.10D. Similarly, the exemplary structure of FIG. 10E may further includea layer of the third type of material 200 formed adjacent to the layerof the second type of material 202 opposite the first stack as shown inFIG. 10B.

FIGS. 10F-10I show some exemplary structures in which one or moreadditional layers are formed adjacent to the n^(th) stack. The exemplarystructures of FIGS. 10G and 10I respectively show that a layer of thefirst type of material 204 and a layer of the second type of material202 may form adjacent to the third type of material 198 of the n^(th)stack. The exemplary structure of FIG. 10G may further include a layerof the second type of material 202 formed adjacent to the layer of thefirst type of material 204 opposite the n^(th) stack as shown in FIG.10H. Similarly, the exemplary structure of FIG. 10I may further includea layer of the first type of material 204 formed adjacent to the layerof the second type of material 202 opposite the n^(th) stack as shown inFIG. 10F.

The multilayer structure of FIG. 10A is not limited to the exemplarystructures of FIGS. 10B-10I and may be constructed from a combination ofthe exemplary structures of FIGS. 10B-10I. For example, the multilayeredstructure of FIG. 10A may have a layer of the third type of material 200formed adjacent to the first stack and a layer of the first type ofmaterial 204 formed adjacent to the n^(th) stack by combining theexemplary structures of FIGS. 10C and 10G. The layer of the first typeof material 194 in a stack 192 may have a different thickness comparedwith other layers of the first type of material in other stacks. Thelayer of the second type of material 196 in a stack 192 may also have adifferent thickness compared with other layers of the second type ofmaterial in other stacks. Similarly, the layer of the third type ofmaterial 198 in a stack 192 may have a different thickness compared withother layers of the third type of material in other stacks. One or morelayers of the three layers of materials 194-198 may be extremely thinand thus have fragmented coverage and/or are perforated with holes. Thelayer thicknesses of the first, second, and third types of materials204, 202, and 200 at the periphery may or may not be same as the layerthicknesses of the first, second, and third types of materials 194, 196,and 198 of the trilayer unit structure 192, respectively. The stackingsequences of the exemplary multilayer structures of FIGS. 10A-10I may beinverted.

Each of the first type of material 194 and 204, the second type ofmaterial 196 and 202, and the third type of material 198 and 200 may bemade of any suitable material, such as but not limited to Co, Ni, Fe,CoNi, CoFe, NiFe, CoNiFe, Pt, Pd, Ni, Ir, Cr, V, Ti, Zr, Hf, Nb, Ta, Mo,W, NiCr, NiV, NiTi, NiZr, NiHf, NiNb, NiTa, NiMo, NiW, or anycombination thereof. Therefore, one or more of the magnetic layers152-156, 160-166, 170-176, and 180 may include a multilayer structure,such as but not limited to [Co/Cr/Ni], [Co/Ni/Cr], [Co/Ir/Ni],[Co/Ni/Ir], [Ni/Co/Cr], [Ni/Cr/Co], [Ni/Co/Ir], [Ni/Ir/Co], [Co/V/Ni],[Co/Ni/V], [Ni/Co/V], [Ni/V/Co], [Co/Cr/Pt], [Co/Cr/Pd], [Co/Cr/Ir],[CoFe/Cr/Ni], [CoFe/Pd/Ni], [CoFe/V/Ni], [CoFe/Ir/Ni], [Co/NiCr/Ni], orany combination thereof. The multilayer structure may have aface-centered cubic (FCC) type of lattice structure, which is differentfrom the body-centered cubic structure (BCC) of some ferromagneticmaterials, such as Fe, CoFe, and CoFeB, and the halite-like cubiclattice structure of magnesium oxide (MgO) that may be used as theinsulating tunnel junction layer 140. All individual magnetic layers ofa magnetic multilayer structure may have the same magnetizationdirection. The multilayer structure may or may not exhibit thecharacteristic satellite peaks associated with superlattice whenanalyzed by X-ray, neutron diffraction, or other diffraction techniques.

One or more of the magnetic layers 152-156, 160-166, 170-176, and 180may alternatively have a multilayer structure formed by one (n=1) ormore stacks of a quadlayer unit structure 206 as illustrated in FIG. 11.The quadlayer unit structure 206 includes a layer of a first type ofmaterial 208, a layer of a second type of material 210, a layer of athird type of material 212, and a layer of a fourth type of material 214formed adjacent to each other. At least one of the four types ofmaterials 208-214 is magnetic. One or more layers of the four layers ofmaterials 208-214 may be extremely thin and thus have fragmentedcoverage and/or are perforated with holes. The multilayer structure ofFIG. 11 may include one or more additional layers made of the first,second, third, and fourth types of materials formed adjacent to thefirst stack and/or the n^(th) stack thereof. The stacking sequence ofthe multilayer structure of FIG. 11 may be inverted. All individualmagnetic layers of the magnetic multilayer structure may have the samemagnetization direction.

Each of the first, second, third, and fourth types of materials 208-214may be made of any suitable material, such as but not limited to Co, Ni,Fe, CoNi, CoFe, NiFe, CoNiFe, Pt, Pd, Ni, Ir, Cr, V, Ti, Zr, Hf, Nb, Ta,Mo, W, NiCr, NiV, NiTi, NiZr, NiHf, NiNb, NiTa, NiMo, NiW, or anycombination thereof. Moreover, two of the four types of materials208-214 not in contact may have the same composition. For example, thefirst and third types of materials 208 and 212 or the second and fourthtypes of materials 210 and 214 may have the same composition. Therefore,one or more of the magnetic layers 152-156, 160-166, 170-176, and 180may include a multilayer structure, such as but not limited to[Ni/Co/Ni/Cr], [Co/Ni/Co/Cr], [Co/Cr/Ni/Cr], [Ni/Co/Ni/Ir],[Co/Ni/Co/Ir], [Co/Ir/Ni/Ir], [Co/Ir/Ni/Cr], [Co/Ir/Co/Cr], or anycombination thereof. The layer of each of the first, second, third, andfourth types of materials 208-214 in a stack 206 may have a differentthickness compared with the layers of the same type of material in otherstacks. The multilayer structure may or may not exhibit thecharacteristic satellite peaks associated with superlattice whenanalyzed by X-ray, neutron diffraction, or other diffraction techniques.

The insulating tunnel junction layer 140 of the MTJ structures 130 and130′ in FIGS. 5A and 5B, respectively, may be formed of a suitableinsulating material containing oxygen, nitrogen, or both, such as butnot limited to magnesium oxide (MgO_(x)), aluminum oxide (AlO_(x)),titanium oxide (TiO_(x)), zirconium oxide (ZrO_(x)), hafnium oxide(HfO_(x)), vanadium oxide (VO_(x)), tantalum oxide (TaO_(x)), chromiumoxide (CrO_(x)), molybdenum oxide (MoO_(x)), tungsten oxide (WO_(x)),gallium oxide (GaO_(x)), silicon oxide (SiO_(x)), silicon nitride(SiN_(x)), MgTiO_(x), MgAlO_(x), AlTiO_(x), or any combination thereof.The insulating tunnel junction layer 140 may have a composite structurecomprising two layers of insulating materials, each of which is made ofa suitable insulating material as described above. For example, thecomposite tunnel junction layer may include a layer of magnesium oxideand a layer of titanium oxide.

The anti-ferromagnetic coupling layer 142 of the MTJ structures 130 and130′ shown in FIGS. 5A and 5B, respectively, may be made of a suitablecoupling material, such as but not limited to ruthenium (Ru), vanadium(V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo),tungsten (W), manganese (Mn), rhenium (Re), osmium (Os), rhodium (Rh),iridium (Ir), copper (Cu), or any combination thereof. Theanti-ferromagnetic coupling layer 142 may have a composite structurethat includes two or more sublayers. Each of the sublayers may be madeof a suitable coupling material described above.

The perpendicular enhancement layers (PELs) 158, 168, and 178 maycomprise one or more of the following elements: B, Mg, Ti, Zr, Hf, V,Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag,Au, Al, Si, Ge, Ga, O, N, and C, thereby forming a suitableperpendicular enhancement material, such as but not limited to B, Mg,Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni,Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga, MgO_(x), TiO_(x), ZrO_(x), HfO_(x),VO_(x), NbO_(x), TaO_(x), CrO_(x), MoO_(x), WO_(x), RhO_(x), NiO_(x),PdO_(x), PtO_(x), CuO_(x), AgO_(x), RuO_(x), SiO_(x), TiN_(x), ZrN_(x),HfN_(x), VN_(x), NbN_(x), TaN_(x), CrN_(x), MoN_(x), WN_(x), NiN_(x),PdN_(x), PtO_(x), RuN_(x), SiN_(x), TiO_(x)N_(y), ZrO_(x)N_(y),HfO_(x)N_(y), VO_(x)N_(y), NbO_(x)N_(y), TaO_(x)N_(y), CrO_(x)N_(y),MoO_(x)N_(y), WO_(x)N_(y), NiO_(x)N_(y), PdO_(x)N_(y), PtO_(x)N_(y),RuO_(x)N_(y), SiO_(x)N_(y), TiRuO_(x), ZrRuO_(x), HfRuO_(x), VRuO_(x),NbRuO_(x), TaRuO_(x), CrRuO_(x), MoRuO_(x), WRuO_(x), RhRuO_(x),NiRuO_(x), PdRuO_(x), PtRuO_(x), CuRuO_(x), AgRuO_(x), CoFeB, CoFe,NiFe, CoFeNi, CoTi, CoZr, CoHf, CoV, CoNb, CoTa, CoFeTa, CoCr, CoMo,CoW, NiCr, NiTi, NiZr, NiHf, NiV, NiNb, NiTa, NiMo, NiW, CoNiTa, CoNiCr,CoNiTi, FeTi, FeZr, FeHf, FeV, FeNb, FeTa, FeCr, FeMo, FeW, or anycombination thereof. In cases where the perpendicular enhancementmaterial contains one or more ferromagnetic elements, such as Co, Fe,and Ni, the total content of the ferromagnetic elements of theperpendicular enhancement material may be less than the thresholdrequired for becoming magnetic, thereby rendering the materialessentially non-magnetic. Alternatively, the perpendicular enhancementmaterial that contains one or more ferromagnetic elements may be verythin, thereby rendering the material superparamagnetic or magneticallydead. One or more of the PELs 158, 168, and 178 may have a multilayerstructure comprising two or more layers of perpendicular enhancementsublayers, each of which is made of a suitable perpendicular enhancementmaterial described above. For example and without limitation, one ormore of the PELs 158, 168, and 178 may have a bilayer structure, such asbut not limited to W/Ta, Ta/W, Mo/Ta, Ta/Mo, W/Hf, Hf/W, Mo/Hf, orHf/Mo.

The seed layer structure 132 of the exemplary magnetic structures shownin FIGS. 5A and 5B, respectively, may include one or more seed layers asillustrated by the exemplary embodiments shown in FIGS. 12A-12D. FIG.12A shows the seed layer structure 132 including a first seed layer 220formed beneath the magnetic fixed layer structure 144 or the magneticfree layer structure 136. A second seed layer 222 may be formed adjacentto the first seed layer 220 opposite the magnetic fixed layer structure144 or the magnetic free layer structure 136 as shown in FIG. 12B.Similarly, a third seed layer 224 may be formed adjacent to the secondseed layer 222 opposite the first seed layer 220 as shown in FIG. 12C,and a fourth seed layer 226 may be formed adjacent to the third seedlayer 224 opposite the second seed layer 222 as shown in FIG. 12D, andso forth. The seed layer structure 132 is not limited to the exemplarystructures of FIGS. 12A-12D and may have additional seed layers notshown.

The first, second, third, and fourth seed layers 220-226 may be made ofany suitable seed layer materials or structures. One or more of the seedlayers 220-226 may comprise one or more of the following elements: B,Mg, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir,Ni, Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga, O, N, and C, thereby forming asuitable seed material such as one of those discussed above for theperpendicular enhancement material. For example and without limitation,one or more of the seed layers 220-226 may be made of AlO_(x) TiO_(x),MgO, CoFeB, CoCr, CoTa, CoTi, CoV, Ta, Ir, Hf, W, Mo, Ru, Pt, Pd, Ti, V,Cr, Zr, Nb, NiCr, NiTa, NiTi, NiV, or TaN. In an embodiment, the seedlayer structure 132 has a bilayer structure (first seed layer 220/secondseed layer 222), such as but not limited to NiTa/NiCr, NiCr/NiTa,NiTi/NiCr, NiCr/NiTi, NiTa/NiTi, NiTi/NiTa, NiV/NiCr, NiCr/NiV, Ta/Ru,Ru/Ta, Hf/Ta, Ta/Hf, W/Ta, Ta/W, W/Hf, Hf/W, Ta/Mo, Mo/Ta, Ta/TaN,TaN/Ta, Ta/TiN, TiN/Ta, Mo/Hf, Hf/Mo, W/Ru, Ru/W, Ir/Ta, Ta/Ir, Ir/W,W/Ir, Ir/Hf, Hf/Ir, Ir/Mo, Mo/Ir, Ir/Pt, Pt/Ir, Ir/Pd, Pd/Ir, MgO/Ta,Ta/MgO, MgO/Ru, Ru/MgO, MgO/Hf, Hf/MgO, MgO/W, W/MgO, MgO/Mo, Mo/MgO,MgO/Ti, Ti/MgO, MgO/V, V/MgO, MgO/Cr, Cr/MgO, MgO/Zr, Zr/MgO, MgO/Nb,Nb/MgO, MgO/Ir, Ir/MgO, or MgO/CoFeB. In another embodiment, the seedlayer structure 132 has a trilayer structure (first seed layer220/second seed layer 222/third seed layer 224), such as but not limitedto MgO/CoFeB/Ru, MgO/CoFeB/Ta, MgO/CoFeB/W, MgO/CoFeB/Hf, MgO/Ru/Ta,MgO/Ru/TaN, Ta/Ru/TaN, or Ru/Ta/TaN. In still another embodiment, theseed layer structure 132 has a quadlayer structure (first seed layer220/second seed layer 222/third seed layer 224/fourth seed layer 226),such as but not limited to MgO/CoFeB/Ru/Ta, MgO/CoFeB/Ta/Ru,MgO/CoFeB/Ta/W, MgO/CoFeB/W/Ta, MgO/CoFeB/Ru/W, MgO/CoFeB/W/Ru,MgO/CoFeB/Hf/Ta, MgO/CoFeB/Ta/Hf, MgO/CoFeB/Hf/W, MgO/CoFeB/W/Hf,MgO/CoFeB/Hf/Ru, MgO/CoFeB/Ru/Hf, MgO/CoFeB/Ta/TaN, or MgO/CoFeB/Ru/TaN.A seed layer that includes one or more ferromagnetic elements may benon-magnetic if the total content of the ferromagnetic elements is lessthan the threshold required for becoming magnetic or if the layerthickness decreases to a point that the supposedly ferromagneticmaterial becomes superparamagnetic. In an embodiment, one or more of theseed layers 220-226 may have a noncrystalline or amorphous structure.

Alternatively, one or more of the seed layers 220-226 may have amultilayer structure formed by interleaving one or more layers of afirst type of seed material 242 with one or more layers of a second typeof seed material 244 as illustrated in FIGS. 13A-13D. FIG. 13A shows anexemplary multilayer seed structure formed by one (n=1) or more stacksof a bilayer unit structure 246, which includes a layer of the firsttype of seed material 242 and a layer of the second type of seedmaterial 244. The multilayer seed structure may include additionallayers formed at the periphery of the exemplary multilayer structure ofFIG. 13A. For example and without limitation, the stacks of the bilayerunit structure 246 may include another layer of the second type of seedmaterial 248 formed adjacent to the first type of seed material 242 ofthe first stack as shown in FIG. 13B, or another layer of the first typeof seed material 250 formed adjacent to the second type of seed material244 of the n^(th) stack (the end stack) as shown in FIG. 13C, or both asshown in FIG. 13D. The layer of the first type of seed material 242 in astack 246 may have a different thickness compared with other layers ofthe first type of seed material in other stacks. Similarly, the layer ofthe second type of seed material 244 in a stack 246 may have a differentthickness compared with other layers of the second type of seed materialin other stacks. The layer thicknesses of the first type of seedmaterial 250 and the second type of seed material 248 at the peripherymay or may not be same as the layer thicknesses of the first type ofseed material 242 and the second type of seed material 244 of thebilayer unit structure 246, respectively. One or more layers of the twotypes of seed materials 242, 244, 248, and 250 may be extremely thin andthus have fragmented coverage and/or are perforated with holes. Thestacking sequences of the exemplary multilayer structures of FIGS.13A-13D may be inverted.

The first type of seed material 242 and 250 may comprise one or more ofthe following non-magnetic elements: B, Mg, Ti, Zr, Hf, V, Nb, Ta, Cr,Mo, W, Mn, Re, Ru, Os, Rh, Ir, Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga, O, N,and C, to form a suitable seed material, such as but not limited to MgO,Ta, Ir, Hf, W, Mo, Ru, Pt, Pd, Ti, Zr, V, Nb, Cr, TiN, and TaN.

Alternatively, the first type of seed material 242 and 250 may compriseone or more ferromagnetic elements, such as but not limited to cobalt(Co), nickel (Ni), and iron (Fe), to form a material, such as but notlimited to Co, Ni, Fe, CoNi, CoFe, NiFe, CoNiFe. The first type of seedmaterial 242 and 250 containing ferromagnetic elements may furtherinclude at least one non-magnetic element, such as but not limited toboron (B), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V),niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten(W), aluminum (Al), silicon (Si), germanium (Ge), gallium (Ga), oxygen(O), nitrogen (N), carbon (C), platinum (Pt), palladium (Pd), ruthenium(Ru), and phosphorus (P), to form an alloy or compound, such as but notlimited to nickel-chromium (NiCr), nickel-titanium (NiTi),nickel-tantalum (NiTa), nickel-vanadium (NiV), nickel-zirconium (NiZr),cobalt-chromium (CoCr), cobalt-titanium (CoTi), cobalt-tantalum (CoTa),cobalt-vanadium (CoV), cobalt-iron-boron (CoFeB),cobalt-iron-boron-titanium (CoFeBTi), cobalt-iron-boron-zirconium,(CoFeBZr), cobalt-iron-boron-hafnium (CoFeBHf),cobalt-iron-boron-vanadium (CoFeBV), cobalt-iron-boron-tantalum(CoFeBTa), cobalt-iron-boron-chromium (CoFeBCr), cobalt-iron-titanium(CoFeTi), cobalt-iron-zirconium (CoFeZr), cobalt-iron-hafnium (CoFeHf),cobalt-iron-vanadium (CoFeV), cobalt-iron-niobium (CoFeNb),cobalt-iron-tantalum (CoFeTa), cobalt-iron-chromium (CoFeCr),cobalt-iron-molybdenum (CoFeMo), cobalt-iron-tungsten (CoFeW),cobalt-iron-aluminum (CoFeAl), cobalt-iron-silicon (CoFeSi),cobalt-iron-germanium (CoFeGe), iron-zirconium-boron (FeZrB) orcobalt-iron-phosphorous (CoFeP). The first type of seed material 242 and250 may be non-magnetic if the content of the magnetic elements is belowthe threshold required for becoming magnetized.

The first type of seed material 242 and 250 may have a layer thicknessof at least about 0.1 nm, preferably about 0.2 to 3.0 nm, morepreferably about 0.2 nm to 2.5 nm. Accordingly, in embodiments where thefirst type of seed material 242 and 250 includes therein ferromagneticelements, the first type of seed material 242 and 250 may becomenon-magnetic or behave like a magnetic dead layer when the thicknessdecreases to a point that the supposedly ferromagnetic material becomessuperparamagnetic.

The second type of seed material 244 and 248 may be made of any suitablematerial for the first type of seed material 242 and 250 as describedabove and may have the same thickness ranges as the first type of seedmaterial 242 and 250 as described above. For example and withoutlimitation, the bilayer unit structure 246 (first type/second type) maybe Ni/Ta, Ni/Ti, Ni/Cr, Ni/V, Ni/Zr, Ni/Hf, Ni/V, Ni/Nb, Ni/Mo, Ni/W,NiCr/Ta, NiCr/Ti, NiCr/V, NiCr/Nb, NiCr/Cr, Co/Ta, Co/Ti, Co/Cr, Co/V,Co/Zr, Co/Hf, Co/V, Co/Nb, Co/Mo, Co/W CoFeB/Ta, CoFeB/Ru, Ru/CoFeB,CoFeB/FeZrB, FeZrB/CoFeB, FeZrB/Ta, Ta/FeZrB, Ni/Ir, NiCr/Ir, Ir/Ta,Ir/Cr, Co/Ir, or CoFeB/Ir, MgO/Ta, MgO/Ru, MgO/Cr, MgO/Ti, MgO/Hf,MgO/Mo, MgO/Ir, Ir/Mo, Ir/W, Ir/Hf, Ir/Zr, Ir/Ti, Ir/Nb, Ir/V, Ir/Ru,MgO/Pt, MgO/Pd, Pt/Ta, Pt/Ti, Pt/Cr, Pt/V, Pt/Zr, Pt/Hf, Pt/V, Pt/Nb,Pt/Mo, Pt/W, Pd/Ta, Pd/Ti, Pd/Cr, Pd/V, Pd/Zr, Pd/Hf, Pd/V, Pd/Nb,Pd/Mo, or Pd/W. In an embodiment, one or both of the first and secondtypes of seed materials 242, 244, 248, and 250 are amorphous ornoncrystalline.

One or more of the seed layers 220-226 of the seed layer structure 132shown in FIGS. 5A and 5B may therefore have a multilayer structureformed by interleaving one or more layers of a first type of seedmaterial 242 with one or more layers of a second type of seed material244. For example and without limitation, the seed layer structure 132may have a structure illustrated in FIG. 12B that includes the secondseed layer 222 made of NiCr or CoCr and the first seed layer 220 formedby interleaving one or more layers of Ni with one or more layers of Ta.The stacking of [Ni/Ta] multilayer structure may begin with a Ni or Talayer and end with a Ni or Ta layer.

The cap layer structure 134 of the exemplary magnetic structures shownin FIGS. 5A and 5B, respectively, may include one or more cap layers asillustrated by the exemplary embodiments shown in FIGS. 14A-14D. FIG.14A shows the cap layer structure 134 including a first cap layer 260formed above the magnetic fixed layer structure 144 or the magnetic freelayer structure 136. A second cap layer 262 may be formed adjacent tothe first cap layer 260 opposite the magnetic fixed layer structure 144or the magnetic free layer structure 136 as shown in FIG. 14B.Similarly, a third cap layer 264 may be formed adjacent to the secondcap layer 262 opposite the first cap layer 260 as shown in FIG. 14C, anda fourth cap layer 266 may be formed adjacent to the third cap layer 264opposite the second cap layer 262 as shown in FIG. 14D, and so forth.The cap layer structure 134 is not limited to the exemplary structuresof FIGS. 14A-14D and may have additional cap layers not shown.

The first, second, third, and fourth cap layers 260-266 may be made ofany suitable cap layer materials or structures. One or more of the caplayers 260-266 may comprise one or more of the following elements: B,Mg, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Rh, Ir,Ni, Pd, Pt, Cu, Ag, Au, Al, Si, Ge, Ga, O, N, and C, thereby forming asuitable cap material such as one of those discussed above for theperpendicular enhancement material. For example and without limitation,one or more of the cap layers 260-266 may be made of AlO_(x) TiO_(x),MgO, CoFeB, CoCr, CoTa, CoTi, CoV, Ta, Ir, Hf, W, Mo, Ru, Pt, Pd, Ti, V,Cr, Zr, Nb, NiCr, NiTa, NiTi, NiV, or TaN. In an embodiment, the caplayer structure 134 has a bilayer structure (first cap layer 260/secondcap layer 262), such as but not limited to NiTa/NiCr, NiCr/NiTa,NiTi/NiCr, NiTa/NiTi, NiTi/NiTa, NiV/NiCr, NiCr/NiV, Ta/Ru, Ru/Ta,Hf/Ta, Ta/Hf, W/Ta, Ta/W, W/Hf, Hf/W, Ta/Mo, Mo/Ta, Ta/TaN, TaN/Ta,Ta/TiN, TiN/Ta, Mo/Hf, Hf/Mo, W/Ru, Ru/W, Ir/Ta, Ta/Ir, Ir/W, W/Ir,Ir/Hf, Hf/Ir, Ir/Mo, Mo/Ir, Ir/Pt, Pt/Ir, Ir/Pd, Pd/Ir, MgO/Ta, Ta/MgO,MgO/Ru, Ru/MgO, MgO/Hf, Hf/MgO, MgO/W, W/MgO, MgO/Mo, Mo/MgO, MgO/Ti,Ti/MgO, MgO/V, V/MgO, MgO/Cr, Cr/MgO, MgO/Zr, Zr/MgO, MgO/Nb, Nb/MgO,MgO/Ir, Ir/MgO, or MgO/CoFeB. The CoFeB layer in the cap layer structure134 may be non-magnetic or superparamagnetic.

Additional cap layers may further form adjacent to the exemplaryMgO/CoFeB cap layer structure to form trilayer cap layer structures(first cap layer 260/second cap layer 262/third cap layer 264), such asbut not limited to MgO/CoFeB/Ru, MgO/CoFeB/Ta, MgO/CoFeB/W,MgO/CoFeB/Hf, MgO/CoFeB/Mo, Mo/MgO/CoFeB, W/MgO/CoFeB, Ta/MgO/CoFeB,Hf/MgO/CoFeB, and Ir/MgO/CoFeB. Other examples of the trilayer structureincludes MgO/Ru/Ta, MgO/Ru/TaN, Ta/Ru/TaN, Ru/Ta/TaN, Ir/Ta/MgO,Ir/Mo/MgO, Ir/W/MgO, Ir/Hf/MgO, Ir/Ru/MgO and Ir/MgO/Ru.

In another embodiment, the cap layer structure 134 has a quadlayerstructure (first cap layer 260/second cap layer 262/third cap layer264/fourth cap layer 266), such as but not limited to MgO/CoFeB/Ru/Ta,MgO/CoFeB/Ta/Ru, MgO/CoFeB/Ta/W, MgO/CoFeB/W/Ta, MgO/CoFeB/Ru/W,MgO/CoFeB/W/Ru, MgO/CoFeB/Hf/Ta, MgO/CoFeB/Ta/Hf, MgO/CoFeB/Hf/W,MgO/CoFeB/W/Hf, MgO/CoFeB/Hf/Ru, MgO/CoFeB/Ru/Hf, MgO/CoFeB/Ta/TaN,MgO/CoFeB/Ru/TaN, Mo/MgO/CoFeB/Ta, W/MgO/CoFeB/Ta, Ta/MgO/CoFeB/Ta,Ir/MgO/CoFeB/Ta, or Hf/MgO/CoFeB/Ta.

A cap layer that includes one or more ferromagnetic elements may benon-magnetic if the total content of the ferromagnetic elements is lessthan the threshold required for becoming magnetic or if the layerthickness decreases to a point that the supposedly ferromagneticmaterial becomes superparamagnetic. In an embodiment, one or more of thecap layers 260-266 may have a noncrystalline or amorphous structure.

FIG. 15 shows an exemplary magnetic structure corresponding to theexemplary embodiment of FIG. 5A. The exemplary structure of FIG. 15includes the seed layer structure 132 and the magnetic fixed layerstructure 144 formed thereon. The magnetic reference layer structure 138is anti-ferromagnetically coupled to the magnetic fixed layer structure144 via the anti-ferromagnetic coupling layer 142. The magnetic freelayer structure 136 is separated from the magnetic reference layerstructure 138 by the insulating tunnel junction layer 140. The cap layerstructure 134 is formed on top of the magnetic free layer structure 136.

With continuing reference to FIG. 15, the seed layer structure 132 mayinclude the second seed layer 222 made of NiCr alloy or compound and thefirst seed layer 220 formed by interleaving one or more layers of Niwith one or more layers of Ta on top of the second seed layer 222. Thesecond seed layer 222 may alternatively be made of NiTa, NiTi, NiV,CoCr, CoTa, CoTi, or CoV. Despite incorporating a ferromagnetic element(Ni or Co) therein, the second seed layer 222 may be non-magnetic. Thefirst seed layer 220 may alternatively be formed by interleaving one ormore layers of Ni or Co with one or more layers of Ti, Ta, or V.Similarly, the first seed layer 220 may be non-magnetic despiteinclusion of one or more Ni or Co layers.

The magnetic fixed layer structure 144 formed on top of the first seedlayer 220 may include multiple layers of Co interleaved with multiplelayers of Ni or Pt. The magnetic fixed layer structure 144 mayalternatively include the first and second magnetic fixed layers 172 and174 with the PEL 178 interposed therebetween. The first and secondmagnetic fixed layers 172 and 174 may each include one or more layers ofCo interleaved with one or more layers of Ni, and the PEL 178 may bemade of Cr.

The anti-ferromagnetic coupling layer 142 formed on top of the magneticfixed layer structure 144 may be made of Ru, Ir, or any combinationthereof. The magnetic reference layer structure 138 formed on top of theanti-ferromagnetic coupling layer 142 includes the first and secondmagnetic reference layers 162 and 164 with the PEL 168 interposedtherebetween. The second magnetic reference layer 164 formed adjacent tothe anti-ferromagnetic coupling layer 142 may include one or more layersof Co interleaved with one or more layers of Pt or Ni. The PEL 168 maybe made of Ta, Mo, W, Hf, or any combination thereof. The first magneticreference layer 162 may comprise Co, Fe, and B. The insulating tunneljunction layer 140 formed on top of the first magnetic reference layer162 may be made of magnesium oxide, aluminum oxide, titanium oxide, orany combination thereof. The magnetic free layer structure 136 formed ontop of the insulating tunnel junction layer 140 may comprise Co, Fe, andB. Alternatively, the magnetic free layer structure 136 may include twoCoFeB layers with a Mo or W PEL interposed therebetween. The cap layerstructure 134 includes the first cap layer 240 formed on top of themagnetic free layer structure 136 and the second cap layer 242 formed ontop of the first cap layer 240. The first and second cap layers 260 and262 may be made of MgO and CoFeB, respectively. In an embodiment, theCoFeB cap layer is non-magnetic.

While the present invention has been shown and described with referenceto certain preferred embodiments, it is to be understood that thoseskilled in the art will no doubt devise certain alterations andmodifications thereto which nevertheless include the true spirit andscope of the present invention. Thus the scope of the invention shouldbe determined by the appended claims and their legal equivalents, ratherthan by examples given.

What is claimed is:
 1. A magnetic structure comprising: a seed layerstructure including one or more layers of a first transition metalinterleaved with one or more layers of a second transition metal; and amagnetic fixed layer structure formed adjacent to said seed layerstructure and having a first invariable magnetization directionsubstantially perpendicular to a layer plane of said magnetic fixedlayer structure, said magnetic fixed layer structure including layers ofa first magnetic material interleaved with layers of said firsttransition metal.
 2. The magnetic structure of claim 1, wherein saidfirst transition metal is nickel.
 3. The magnetic structure of claim 1,wherein said first transition metal is iridium.
 4. The magneticstructure of claim 1, wherein said first transition metal is platinum.5. The magnetic structure of claim 1, wherein said first transitionmetal is palladium.
 6. The magnetic structure of claim 1, wherein saidsecond transition metal is tantalum.
 7. The magnetic structure of claim1, wherein said second transition metal is titanium or vanadium.
 8. Themagnetic structure of claim 1, wherein said second transition metal ishafnium or zirconium.
 9. The magnetic structure of claim 1, wherein saidsecond transition metal is molybdenum or tungsten.
 10. The magneticstructure of claim 1, wherein said first magnetic material is cobalt.11. The magnetic structure of claim 1, wherein said first magneticmaterial and said first transition metal are cobalt and nickel,respectively.
 12. The magnetic structure of claim 1, wherein said firstmagnetic material and said first transition metal are cobalt andiridium, respectively.
 13. The magnetic structure of claim 1, whereinsaid first magnetic material and said first transition metal are cobaltand platinum, respectively.
 14. The magnetic structure of claim 1,wherein said seed layer structure is non-magnetic.
 15. The magneticstructure of claim 1, wherein said magnetic fixed layer structureincludes a first magnetic fixed layer and a second magnetic fixed layerwith a first perpendicular enhancement layer (PEL) interposedtherebetween, each of said first and second magnetic fixed layersincluding one or more layers of said first magnetic material interleavedwith one or more layers of said first transition metal.
 16. The magneticstructure of claim 15, wherein said first PEL is made of chromium. 17.The magnetic structure of claim 1 further comprising: ananti-ferromagnetic coupling layer formed adjacent to said magnetic fixedlayer structure opposite said seed layer structure; and a magneticreference layer structure formed adjacent to said anti-ferromagneticcoupling layer, said magnetic reference layer structure having a secondinvariable magnetization direction that is substantially perpendicularto a layer plane thereof and is substantially opposite to said firstinvariable magnetization direction, wherein said magnetic referencelayer structure includes a first magnetic reference layer and a secondmagnetic reference layer with a second perpendicular enhancement layer(PEL) interposed therebetween, said second magnetic reference layerformed adjacent to said anti-ferromagnetic coupling layer opposite saidmagnetic fixed layer structure and including one or more layers of asecond magnetic material interleaved with one or more layers of a thirdtransition metal.
 18. The magnetic structure of claim 17, wherein saidsecond magnetic material and said third transition metal are cobalt andplatinum, respectively.
 19. The magnetic structure of claim 17, whereinsaid anti-ferromagnetic coupling layer is made of iridium.
 20. Themagnetic structure of claim 17 further comprising: an insulating tunneljunction layer formed adjacent to said first magnetic reference layer;and a magnetic free layer structure formed adjacent to said insulatingtunnel junction layer and including one or more magnetic free layersthat have a variable magnetization direction substantially perpendicularto layer planes thereof.
 21. The magnetic structure of claim 20, whereinsaid magnetic free layer structure includes a first magnetic free layerand a second magnetic free layer with a third perpendicular enhancementlayer (PEL) interposed therebetween.